INHIBITORY EFFECT OF TANNIC-ACID ON GASTRIC H+,K+-ATPASE

The effect of tannic acid on gastric H+,K+-ATPase was studied. Tannic acid dose-dependently inhibited pig gastric H+,K+-ATPase activity with an IC50 value of 2.9 x 10(-8) M. Tannic acid also inhibited K+-stimulated p-nitrophenyl phosphatase (K+-pNPPase) activity, which is found in gastric H+,K+-ATPase preparations, as well as H+,K+-ATPase activity, with an IC50 value of 4.1 x 10(-7) M. Kinetic studies showed that the inhibition of H+,K+-ATPase activity by tannic acid was competitive with respect to ATP and non-competitive with respect to K+. These results show that tannic acid is a potent inhibitor of gastric H+,K+-ATPase; this may be related to its anti-secretory and anti-ulcerogenic effects.